The invention is directed to print media coating devices and methods.
It is sometimes desirable to coat printed media with a film of clear flexible material. Such coatings can be formulated and applied to help protect the printed image, enhance the printed image or provide a more uniform gloss level across the entire media (including both printed and unprinted areas).
Duplex printing, in which printed images are applied to both sides of a sheet of paper or other print media, is now very common. Many printers, copiers, multi-function peripherals and other printing devices offer duplex printing. Where a coating is desired on both sides of a sheet, such as might be the case with duplex printing, the sheet must pass twice through the coating module of a post print finishing devicexe2x80x94once to coat the top of the sheet and once to coat the bottom of the sheet.
The patent application filed on Oct. 25, 2002 under and entitled xe2x80x9cPrint Media Coating Device and Methodxe2x80x9d describes devices and methods for simultaneously coating both sides of printed media with a flexible film. For conventional single side coating, as well as the new two-side coating described in the ""897 patent application, it is desirable to use a peel bar to help separate the film carrier from the film after the film is applied to the media. Coatings are applied to print media by overlaying on the media a multilayered web containing the coating material and then applying heat and pressure to fuse the coating material to the media. The web includes a film/layer of coating material, a carrier (sometimes called a backing), and a release layer in between the coating material and the carrier.
In a conventional single side coating device such as the one illustrated in FIG. 11, the peel bar 2 protrudes slightly into media path 3 downstream from fuser 4 to apply pressure to coating material web 5. Web 5 is threaded through fuser 4 from a supply spool 6 to a take-up spool 7. Coating material web 5 and media sheet 8 are sandwiched together through fuser 4 with the coating material film part of web 5 facing sheet 8. Fuser 4 applies heat and pressure to the web/sheet sandwich to affix the coating material film to the sheet 8. The carrier portion of web 5 angles up off peel bar 2 to take-up spool 7. The point pressure applied by peel bar 2 to web 5 helps the carrier portion of web 5 separate more cleanly from the coating film, now affixed to sheet 8.
In one design of the new two-side coating device, the peel bars are placed directly opposite one another across the media path so that each carrier is peeled away from the coating film at the same time. During the development and testing of this design, it was discovered that the adhesion between the carrier and the coating film is such that each web tends to pull on the sheet as the carrier peels away from the coating film. This pull is not always the same on each side of the sheet. One side pulling harder than the other tends to relieve pressure on the weak side peel bar. This pressure relief can impede separation between the carrier and the coating film on the weak side which can, in turn, effect the quality of the coating film retained on that side of the sheet. Accordingly, the present invention was developed in an effort to maintain a more uniform pressure on each peel bar as a way to improve carrier/coating film separation.
One embodiment of the present invention is directed to a print media coating device that includes first and second web supplies, first and second web take-ups, and a fuser defining a print media path therethrough. The first web supply and the first web take-up are positioned on one side of the media path and the second web supply and the second web take-up are positioned on the other side of the media path opposite the first web supply and the first web take-up. A first coating material web runs from the first web supply, along the media path through the fuser, to the first web take-up and a second coating material web runs from the second web supply, along the media path through the fuser, to the second web take-up. A first peel bar is positioned immediately adjacent to the print media path, downstream from the fuser on the first side of the media path. A second peel bar is positioned immediately adjacent to the print media path downstream from the fuser and downstream from the first peel bar.
Another embodiment of the invention is directed to a method for coating print media that includes: providing first and second coating material webs, each web having a coating material and a carrier carrying the coating material; sandwiching the print media between the first and second coating material webs; fusing coating material to the print media; and peeling the carrier from the coating material on the first coating material web and then peeling the carrier from the coating material on the second coating material web.